The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustions engines combust an air and fuel (A/F) mixture within cylinders to produce drive torque. More specifically, the combustion events reciprocally drive pistons that in turn drive a crankshaft to provide output torque. The A/F mixture is ignited at a desired crank angle. In some instances, however, the A/F mixture auto-ignites ahead of an ignition flame-front within the cylinders. This results in abnormal combustion or engine knock.
During an engine knock condition, temperature and pressure of an unburned air/fuel mixture exceeds a certain level, which causes gases in an engine to auto-ignite. This combustion produces a shock wave that generates a rapid increase in cylinder pressure. Damage to pistons, rings, and exhaust valves can result if sustained heavy engine knock occurs. Engine knock can be heard by vehicle passengers.
Modern engine control systems are designed to minimize exhaust emissions while maximizing power and fuel economy. Advancements in spark timing for a given air/fuel ratio are made to increase power and improve fuel economy. In general, advancing a spark relative to top dead center increases torque until a point is reached at which a peak torque is produced. When the spark is advanced too far, engine knock occurs. Thus, a spark is typically advanced to maximize output torque without generating engine knock.
Accordingly, engine knock control systems have been developed to detect and to mitigate engine knock. Conventional knock detection systems include a knock sensor and a dedicated knock detection chip (knock IC) to process the knock sensor signal and calculate the engine knock intensity. An individual knock sensor and knock IC can be used to detect knock from each cylinder. Spark timing is adjusted based on detected engine knock.
Over time and use an engine knock sensor circuit may experience a short or an open circuit. As a result, signals received from an engine knock sensor may be inaccurate or ineffective in preventing engine knock. Diagnosing a knock sensor circuit is difficult due to intrinsic high resistance and moderate capacitance associated therewith.